1. Field of the Invention
This invention generally relates to a package for electronic components. Specifically, the invention relates to a ball grid array for making electrical connections in an electronic component.
2. Description of the Related Art
Many electronic packages utilize a via to connect one level or layer of circuitry to another. A via is a hole or aperture that is filled with a conductive compound to provide an electrical connection between different planes of a package allowing one side to be electrically connected to another.
The via after processing needs to be very flat in order for subsequent processing steps to succeed. The ends of the via need to be flat and not have a protrusion or a depression. The via also needs to adhere to the side walls of the via hole and not pull away from it after processing.
Prior art vias have suffered from excessive shrinkage during processing that cause depressions to form in the end of the via. The prior art compositions also can cause the via fill material to pull away from the side wall of the via hole resulting in an open circuit.
Ball grid array packages are also well known in the prior art. Typically a solder ball is used to connect between a substrate and a printed circuit board. When used with a ball grid array, ball pads are required to be placed around the vias. A solder paste is placed onto the ball pad with a solder ball and reflowed in an oven. The ball pad allows the solder to spread out around the ball making a uniform connection. The ball pad also helps to spread out the forces that the solder joint sees during thermal cycles ensuring a reliable connection over the life of the package.
Unfortunately, the use of the ball pad takes up valuable real estate and results in a less dense package that contains few connections per unit area. The ball pad also requires additional process steps to fabricate during manufacturing. Purchasing substrates with holes for an electronic package is more expensive than those without holes. It is desirable to have a high density ball grid array package that can eliminate the expense of the holes.
Another problem with prior art electronic packages is that they use lead. Lead is most commonly used in solder to make interconnections between various electronic components. Lead is a known poison to humans and several efforts by government agencies have been proposed to ban its use in electronics. It is desirable to have an electronic package that eliminates the need for lead.
Another problem with prior art electronic packages is that they are susceptible to shorting due to silver migration. Silver migration is the ionic movement of silver in the presence of moisture and an electronic potential. The silver forms a dendrite which can grow until it reaches another conductor causing a short. After the short occurs, the dendrite typically opens due to resistance heating. Silver compositions such as thick film conductors, conductive epoxies and conductive adhesives are known to suffer from silver migration problems.
A current unmet need exists for a ball grid array package that overcomes the deficiencies of the prior art.